I am also facing same issue with my watch os app. Whenever I remove app from device and install new from test flight then I'm not getting location authentication alert in watch os 10 beta. (It's working fine before watch os 10 beta) Right now I'm using following workaround. (This workaround will reset all the apps locations and privacy) Make sure iPhone and watch is connected with Bluetooth. Remove watch app from background. Goto Settings app ->General->Transfer or Reset iPhone->Reset->Reset Location and Privacy. Open watch app again then you will receive location authentication alert.